Microelectronic mounting with multiple lead deformation using restraining straps

ABSTRACT

A microelectronic assembly includes a first microelectronic element including contacts on a contact-bearing face and a second microelectronic element confronting the first microelectronic element. The assembly also has a plurality of vertically extended signal leads electrically interconnecting the first and second microelectronic elements, and a plurality of vertically extended straps attached to the first and second microelectronic elements, whereby the straps are shorter than the signal leads for limiting vertical movement of the first and second microelectronic elements away from one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation of U.S. patentapplication Ser. No. 09/385,320, filed Aug. 30, 1999, which is adivisional of U.S. patent application Ser. No. 08/989,582, filed Dec.12, 1997, which in turn claims benefit of United States ProvisionalApplication Serial Nos. 60/045,690, filed May 6, 1997 and 60/033,066,filed Dec. 12, 1996. The disclosures of the above-mentioned applicationsare hereby incorporated by reference herein.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to methods and components formaking microelectronic assemblies. Complex microelectronic devices suchas modern semiconductor chips require numerous connections to otherelectronic components. For example, a complex microprocessor chip mayrequire many hundreds of connections to external devices.

[0003] As disclosed in U.S. Pat. No. 5,518,964, the disclosure of whichis also incorporated by reference herein, flexible connections can beprovided between microelectronic elements using a process in which theleads are connected between the elements and the elements are then movedthrough a predetermined displacement relative to one another so as todeform the leads. For example, a first element may be a microelectronicconnection component which includes a dielectric element such as aflexible sheet having a bottom surface. A plurality of leads are alsoprovided. Each lead has a terminal end permanently attached to thedielectric element and a tip end remote from the terminal end. Each leadinitially extends in a horizontal plane, generally parallel to thebottom surface of the dielectric sheet. Desirably, the tip ends of theleads are releasably connected to the dielectric element. While theleads are in this condition, the tip ends are attached to a secondelement, such as a further dielectric sheet, a semiconductor chip, asemiconductor wafer or other microelectronic element. After the tip endsof the leads have been attached to the second element, the first andsecond elements are moved away from one another, so that the tip ends ofthe leads are pulled away from the first element and bent to avertically extensive configuration. In this condition, the leads areflexible and allow movement of the first and second elements relative toone another. Preferably, a curable liquid material is introduced betweenthe elements to form a compliant layer therebetween. Thus, in thecompleted assembly the first and second elements are movable relative toone another.

[0004] As further described in the '964 patent, these arrangements offernumerous advantages. The resulting assembly provides mechanicaldecoupling between the elements, and thus provides compensation forthermal expansion and warpage of the elements. The preferred processesaccording to the '964 patent can make a large number of connections in asingle operation. For example, where a wafer incorporating numerouschips is used as one element in the connection process, all of the leadsto all of the chips can be connected in a single set of operations. Theresulting wafer-scale assembly can be severed to provide numerousindividual units, each including one or more chips. Further variations,improvements and adjuncts to the processes and components taught in the'964 patent are also disclosed in U.S. Pat. No. 5,688,716, and incopending, commonly assigned U.S. patent application Nos. 08/532,528Filed Sep. 22, 1995; 08/678,808 Filed Jul. 12, 1996; and 08/690,532Filed Jul. 31, 1996, the disclosures of which are also incorporated byreference herein.

[0005] Despite the advances in the art discussed above, still furtherimprovements would be useful.

SUMMARY OF THE INVENTION

[0006] One aspect of the present invention provides methods of making amicroelectronic assemblies. A method in accordance with this aspect ofthe invention desirably includes the steps of providing a pair ofelements having a plurality of signal leads attached to said elementsand electrically interconnecting said elements, and also having aplurality of straps attached to said elements, said signal leads andsaid straps extending generally in a horizontal direction. The methodfurther includes the step of moving the elements vertically away fromone another so that said straps and said signal leads are bent to avertically extensive disposition. In the moving step, the straps atleast partially constrain movement of the elements relative to oneanother. However, the signal leads most preferably do not constrain thismovement. Stated another way, the straps control the relative movementso that the signal leads are not pulled taut and placed under tensionbetween the elements. Accordingly, little stress is applied to therelatively delicate signal leads and their connections to themicroelectronic elements. The straps may be considerably stronger thansaid signal leads. The straps may also be shorter than the signal leadsso that as the elements move away from one another, the straps will bepulled taut before the signal leads. Typically, the straps are lessnumerous than the signal leads.

[0007] The straps may also be electrically connected to themicroelectronic elements so that the straps further electricallyinterconnect the elements. In a particularly preferred arrangement, theelements include constant-potential connections such as power or groundconnections and some or all of the straps are electrically connectedbetween constant-potential connections on both of said elements. Thus,the straps may serve as power leads, ground leads or both in thefinished assembly.

[0008] The elements may include opposed, horizontally-extending surfacesof said elements confronting one another and the signal leads and saidstraps may be disposed between these opposed surfaces. For example, oneof the elements may be a connection component including a structure suchas a dielectric sheet having a bottom surface, whereas the secondelement may include one or more semiconductor chips having top surfaceswith contacts thereon. The leads and straps may be provided on thebottom surface of the connection component, so that the leads and strapsextend along the bottom surface of the connection component, and theconnection component may be positioned with the bottom surface facingthe top surfaces of the chips. The leads and straps may be connectedbetween the elements by bonding ends of the leads and straps to the topsurfaces of the chips.

[0009] Each strap may have a first end connected to a first one of theelements and a second end connected to a second one of the elements.Before the moving step, the second end of each strap may be offset fromthe first end of that strap in a first horizontal direction. In thisarrangement, the straps will constrain the first element to moverelative to the second element in the first horizontal direction duringthe moving step. Each signal lead may also have first and second endsconnected to the first and second elements, respectively. Prior to themoving step, the second end of each lead may be offset from the firstend of the lead in the first horizontal direction. Thus, the movement ofthe first element with a component of motion in the first horizontaldirection will cause the ends of each said signal lead to movehorizontally towards one another while the lead ends move verticallyaway from one another as the elements move away from one another. Wherethe signal leads are initially straight, this compound movement can bendthe leads into a generally S-shaped configuration.

[0010] The step of moving the elements vertically away from one anothermay include the step of applying a fluid under pressure between opposedsurfaces of the elements so that the fluid forces the elements away fromone another. Because the movement of the elements relative to oneanother is constrained by the straps, there is no need to use externalmechanical elements to control the movement.

[0011] A further aspect of the present invention provides connectioncomponents for making microelectronic assemblies. A connection componentaccording to this aspect of the invention desirably includes astructural element, and a plurality of flexible signal leads, each suchlead having a fixed end permanently attached to the structural elementand a free end detachably secured to the structural element. Thecomponent also includes a plurality of flexible straps. Each strap has afixed end permanently attached to the structural element and a free enddetachably secured to the structural element. Most preferably, thestraps are shorter and stronger than the leads, and the straps aredisposed adjacent the leads. The structural element may have a surfacewith the straps and the leads extending along the surface. The strapsand the leads desirably are disposed in an array on the bottom surfaceand the leads are interspersed with the straps in the array. Thestructural element may be a dielectric element such as a flexibledielectric sheet or may be a semiconductor chip or wafer.

[0012] As discussed above in connection with the method, the free end ofeach the lead may be offset from the fixed end of that lead in a firsthorizontal direction along the bottom surface, and the free end of eachthe strap may be offset from the fixed end of that strap in the samefirst horizontal direction. Components in accordance with this aspect ofthe invention may be used in methods as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a fragmentary diagrammatic bottom view, taken alonglines 1-1 in FIG. 2, depicting the first element used in the structureof FIG. 2.

[0014]FIG. 2 is a fragmentary, diagrammatic sectional elevational viewdepicting first and second elements in accordance with one embodiment ofthe invention after connection of the leads between these elements, butprior to relative movement of these elements.

[0015]FIG. 3 is a view similar to FIG. 1 but depicting the structure ina later stage of the process, during relative movement of the elements.

[0016]FIGS. 4, 5 and 6 are views similar to FIGS. 1, 2 and 3respectively, but depicting elements in accordance with a furtherembodiment of the invention, FIG. 5 being taken along line 5-5 in FIG.4.

[0017]FIG. 7 is a diagrammatic top plan view of an assembly during aprocess in accordance with a further embodiment of the invention.

[0018]FIG. 8 is a diagrammatic sectional view taken along line 8-8 inFIG. 7.

[0019]FIG. 9 is a view similar to FIG. 8 but depicting the assembly in alater stage of the process.

[0020]FIG. 10 is a diagrammatic sectional view of an assembly during aprocess according to a further embodiment of the invention.

[0021]FIG. 11 is a perspective view of a wafer in accordance with afurther embodiment of the invention.

[0022]FIG. 12 is a fragmentary, diagrammatic view of a portion of thewafer depicted in FIG. 11.

DETAILED DESCRIPTION

[0023] An assembly in accordance with one embodiment of the inventionincludes a first element or connection component 10. The connectioncomponent includes a flexible sheet dielectric structure 11 having abottom surface 12, a top surface 14, and a set of conductive power andground planes extending parallel to these surfaces. One such conductiveplane 16 is visible in the drawing figures; the others (not shown)extend inside the dielectric structure or on its surfaces. Thedielectric structure 11 of the connection component may include one ormore sheets of a flexible but substantially inextensible dielectricmaterial such a polyimide or other or other known dimensionally stablepolymeric films used in the semiconductor industry. The dielectric sheetdesirably is about 25-35 microns thick. The conductive planes may beformed as thin, flexible metal layers such as copper layers formed byconventional additive or subtractive plating and etching processes.

[0024] A large number of electrically conductive signal leads 18 areprovided on bottom surface 12. Each signal lead has a terminal end 20and a tip end 22. The terminal end of each lead is permanently securedto the dielectric structure of first element 10. In the particularstructure illustrated, the terminal end of each lead is secured to thedielectric structure by a metallic via structure 24 extending throughthe first element and a terminal 26 integral with the structure 24overlying top surface 14. Because the terminal ends of the leads arepermanently attached to the dielectric structure, the terminal ends arealso referred to herein as the fixed ends of the leads. The viastructures 24 associated with the signal leads extend through holes 30in conductive planes 16, so that the via structures 24 and the signalleads are insulated from the conductive planes 16. Optionally, some ofthe signal leads 18 may be connected to the conductive planes by the viastructures 24 or by other interconnecting elements (not shown).

[0025] The tip end 22 of each lead is provided with a mass of bondingmaterial 28. The tip end of each signal lead 18 is releasably secured tobottom surface 12 of the dielectric sheet 11. As described in greaterdetail in the aforementioned '964 patent, the tip ends of the leads maybe releasably attached to the bottom surface itself by adhesion betweenthe lead material and the bottom surface of the dielectric layer, withina relatively small region disposed between the lead tip end and thebottom surface of the dielectric layer. Alternatively or additionally,the tip ends of the leads may be secured to the bottom surface byfrangible elements or may be bonded to the bottom surface of dielectricsheet by a bonding process which provides a relatively low peelstrength. Low peel strength connections are described in further detailin copending, commonly-assigned U.S. patent application Ser. No.08/547,170, filed Oct. 24, 1995, the disclosure of which is incorporatedby reference herein. Because the tip ends of the leads can be freed fromtheir attachment to the bottom structure or dielectric sheet, the tipends are also referred to herein as free ends.

[0026] In the condition illustrated in FIGS. 1 and 2, each lead 18 iscurved and extends in a horizontal plane substantially parallel to thebottom surface of the dielectric layer. As used in this disclosure withreference to a structure of microelectronic on or associated with asurface of the component, the term “horizontal” refers to the directionparallel to the component surface. As used with reference to a pair ofcomponents having opposed, confronting surfaces, the term “horizontal”refers to the directions along the confronting surfaces. The term“vertical” refers to the direction transverse to the horizontaldirections. Thus, in the case of components having confronting surfaces,the vertical directions are the directions from one component toward theother component.

[0027] Each signal lead 18 desirably is thin and flexible. The leads maybe formed from metallic or other conductive material, alone or inconjunction with a dielectric material such as a polymeric material. Thedimensions of the signal leads may be as described in the '964 patent.For example, where the connection component is intended to connect witha microelectronic component having contacts in a rectilinear grid withrow and column spacings of about 1000 microns, the leads may be on theorder of 35 microns wide, and the distance D₁ between the center of thefixed or terminal end 20 and the center of the free or tip end 22 ofeach lead may be on the order of 500-1000 microns. However, becauseleads 18 are curved, the length of each lead is considerably longer thanthe straight-line distance D₁. As used in this disclosure with referenceto a curved lead or strap, the term “length” should be understood asreferring to the shortest distance between the fixed end and the freeend, measured along the lead itself. Where the lead is curved, theshortest distance along the lead itself normally will not be a straightline.

[0028] A plurality of restraining straps 32 are also provided on thebottom surface 12 of the dielectric sheet or first element 10. As shownin FIG. 2, restraining straps 32 are interspersed in the array of signalleads 18. Thus, the restraining straps are provided at intervals overthe area encompassed by the array of restraining straps. The structureof the restraining straps 32 is generally similar to the structure ofsignal leads 18. Thus, each restraining strap 32 has a fixed or terminalend 34 permanently fastened to the dielectric structure 11 of connectioncomponent 10 by a via structure 36 extending through the dielectricsheet and a terminal 38 on the top surface 14. Each restraining strap 32further has a tip end or free end 40 releasably connected to the bottomsurface 12 of the dielectric sheet, each such tip end being providedwith a bonding material 42. Most or all of the restraining straps 32 areconnected to the potential planes 16, as by interconnection between viastructures 36 and one or more of the potential planes, or by otherconnecting elements (not shown). Different ones of the restrainingstraps 32 may be connected to different potential planes. For example,some of the restraining straps may be connected to a first potentialplane which serves as a power plane whereas other restraining straps 32may be connected to a second potential plane serving as a groundreference plane. The restraining straps 32 are shorter than signal leads18. That is, the length of each restraining strap 32, measured along thestrap itself, in the manner discussed above, is less than the length ofeach signal lead 18. Also, restraining straps 32 have largercross-sectional areas than signal leads 18. For example, the restrainingstraps may have cross-sectional areas about 1.5 times thecross-sectional areas of the signal leads or more. The masses ofconductive bonding material 42 on the tip ends of the restraining strapsmay cover larger areas than the corresponding masses 28 on the tip endsof the signal leads. In short, the restraining straps are of stronger,more robust construction than the signal leads. Typically, the assemblywill include a relatively small number of restraining straps 32 and arelatively large number of signal leads 18. Therefore, any additionalarea consumed by providing relatively large, robust restraining strapswill be minimal.

[0029] In an assembly method according to an embodiment of theinvention, first element or connection component 10, with the leadsthereon, is connected to a second element such as a semiconductor wafer50. Wafer 50 has signal contacts 52 and ground and power referencecontacts 54 distributed over its top surface 56. The tip ends 22 ofsignal leads 18 are connected to the signal contacts 52 whereas the tipends 40 of the restraining straps 32 are connected to the referencecontacts 54. Depending upon the design of the particular chip or wafer,reference contacts 54 may be larger and more robust than the signalcontacts 52. The bottom surface 12 of the first element or connectioncomponent, with the leads and straps thereon, is juxtaposed with the topsurface 56 of the second element or wafer. The elements are aligned withone another so as to align the tip or free end of each lead and eachstrap with a contact on the wafer. The bonding materials on the tip endsof the leads are activated to bond the free or tip ends of the leads andstraps to the contacts. For example, where the bonding materials 28 and42 on the leads and straps include a heat-activatable bonding material,heat may be applied while pressing the dielectric element 11 of theconnection component toward the wafer. The alignment and bonding stepsmay be performed as described in the '964 patent. As further set forthin that patent, the dielectric element may be held taut in a rigidframe, and may be reinforced by a reinforcing element (not shown) on thetop surface 14 to facilitate accurate alignment over the entire area ofthe dielectric element.

[0030] After the free or tip ends of the leads and straps have beenbonded to the contacts, first element 10 and second element 50 are movedwith a component of motion in a vertical direction V away from oneanother. This may be accomplished by injecting a fluid material such asgas or, preferably, a curable liquid 60, under pressure between thefirst and second elements. Movement of the first and second elementsrelative to one another brings the assembly to the condition illustratedin FIG. 3. In this movement, the leads 18 and straps 34 are bentvertically away from the bottom surface of the first element. Thus, thetip end 22 of each lead is moved vertically away from the terminal end20 of the same lead. This movement is accommodated by the initialcurvature of each signal lead, which is partially straightened.Similarly, the tip ends 40 of the restraining straps move verticallyaway from the terminal ends 34 of the restraining straps. Here again,the vertical movement of the tip ends straightens the initial curvatureof the lead. Restraining straps 32 reach a substantially straight, fullyextended condition as illustrated in FIG. 3. In this condition, therestraining straps 32 arrest further vertical movement of first element10 relative to second element 50. Because restraining straps 32 areshorter than signal leads 18, restraining straps 18 will reach thiscondition while signal leads 18 are still slack and still partiallycurved. Thus, the restraining straps constrain the movement of the firstand second elements away from one another, and assure that such movementceases before the signal leads are pulled taut.

[0031] After the moving step is complete, the curable liquid material iscured to form a compliant layer such as a gel or elastomer between thetwo elements. The resulting assembly is then severed, as by sawing theassembly to sever the dielectric element, compliant layer and wafer andform individual units. Each unit includes one or more of thesemiconductor chips included in the wafer or second element 50, togetherwith the overlying portions of the connection component or first element10. Each unit provides a packaged semiconductor chip or assembly ofchips, which may be mounted to a circuit board or other substrate, as bysolder-bonding the terminals 26 and 38 to the substrate. The leads andrestraining straps provide electrical interconnection to the substrate,but allow relative movement of the semiconductor chip and the substrate.The curing and severing steps can be performed as described in greaterdetail in the '964 patent.

[0032] As also discussed in the '964 patent, the leads may be providedon the surface of either element as, for example, on the chip or waferrather than on a dielectric sheet. The same considerations apply to therestraining straps. Also, as described in the '964 patent, the signalleads may be initially straight and the movement of the first and secondelements relative to one another may include both a vertical componentof motion and a horizontal component of motion. In this embodiment aswell, restraining straps in accordance with the present invention may beprovided. Here again, the restraining straps will be shorter than thesignal leads.

[0033] Thus, as shown in FIGS. 4 and 5, straight restraining straps 132and straight signal leads 118 may be provided. The first element 110 andsecond element 150 are connected by bonding the free or tip ends 122 ofthe signal leads to signal contacts on the second element orsemiconductor device 150 and by bonding the free or tip ends 140 ofrestraining straps 132 to contacts such as power or ground contacts onthe second element 150 As shown in FIGS. 4 and 5, all of the leads areinitially straight. The free or tip end 122 of each lead is offset fromthe terminal end 120 of the same lead in a first horizontal direction H.The free end 140 of each restraining strap is also offset in firsthorizontal direction H from the fixed end 134 of the same strap.However, the restraining straps 132 are shorter than the signal leads118.

[0034] As shown in FIG. 6, when the first element 110 and second element150 are moved in a vertical direction V away from one another,restraining straps 132 remain taut. The first element 110 thus moves inan arc generally as indicated by the arcuate arrow A relative to thesecond element. Stated another way, the restraining straps 132 constrainthe movement of the first element relative to the second element andconstrain first element 110 to move in first horizontal direction Hrelative to the second element as the first element moves verticallyaway from the second element. The combined vertical and horizontalmotion deforms each of signal leads 118 into a bent, generally S-shapedconfiguration as shown in FIG. 6. Such horizontal motion will occurwithout the use of mechanical devices to move the two elementshorizontally relative to one another. For example, a fluid such as a gasor, preferably, a curable liquid encapsulant such as an elastomer 151may be injected under pressure between the first and second elements.This pressure will force the elements away from one another in thevertical direction. The restraining straps will constrain the firstelement to move horizontally relative to the second element during thisprocess.

[0035] Although it is advantageous to use the restraining straps aspower or ground connections in the manner discussed above, the same isnot essential. For example, the restraining straps may be connected to“dummy” contacts on the chip or wafer, and may serve no electricalfunction whatsoever. Alternatively or additionally, the restrainingstraps can be used to provide additional signal connections. In thepreferred embodiment, the restraining straps are formed from the samematerials as the signal leads and hence the restraining straps act aselectrically conductive leads. However, in the broad compass of theinvention, it is possible to form the restraining straps fromnonconductive materials such as polymers. The number of restrainingstraps or restraining straps and the placement of these elements on thesurfaces of the elements can be varied. Preferably, where one or both ofthe elements includes a flexible sheet, restraining straps are dispersedat spaced apart locations over substantially the entire extent of thesheets, so that restraining straps limit vertical movement of each areaof the flexible sheet. As disclosed in copending, commonly assigned U.S.Provisional Patent Application No. 60/032,828 filed Dec. 13, 1996, andin the commonly assigned United States Patent Application entitledMicroelectronic Assembly Fabrication With Terminal Formation From AConductive Layer, filed of even date herewith, claiming benefit of said'828 provisional application and naming John W. Smith and JosephFjelstad as inventors, the disclosures of which are incorporated byreference herein, a flexible sheet-like element may be provided with arigid reinforcing element such as a conductive metallic sheet. Aftermovement of the elements to deform the leads, and after formation of acompliant layer between the elements, the rigid reinforcing element canbe etched or otherwise treated to remove metal from it and convert thereinforcing element to electrically conductive parts of the assemblysuch as terminals. This restores flexibility of the flexible element,and allows the terminals to move relative to one another and relative tothe opposite element such as the chip or wafer. These techniques can beused in the present invention. When such a rigid reinforcement isprovided, the flexible sheet-like element will not tend to bulge out ofplane. Therefore, greater spacings can be provided between therestraining straps. Likewise, when both elements are rigid and do nottend to bulge or bend, large spacings can be provided betweenrestraining straps.

[0036] An assembly according to a further embodiment of the inventionincludes a semiconductor chip 250 having rows of contacts 252 along itsedges. The assembly further includes a connection component 210 having adielectric structural element 211 with terminals 226 thereon. In thecondition illustrated in FIGS. 7 and 8, signal leads 218 extendhorizontally outwardly, beyond edges 213 of the dielectric element. Aninner end 220 of each signal lead is fixed to the dielectric structureand electrically connected to a terminal 226 on the dielectric element,whereas the outer or free end 222 of each lead is connected to one ofthe chip contacts 252. The assembly further includes restraining straps232, each having a fixed end 234 permanently fastened to the dielectricelement and a free end 240 bonded to the chip. The restraining strapsare interspersed in the rows of leads. Here again, the restrainingstraps are shorter and stronger than the leads. The leads are curved. Asbest seen in FIG. 8, in the initial, unmoved condition of the assembly,leads 218 are curved in both the vertical and horizontal directions, andextend both vertically and horizontally. Leads 218 may be provided as apart of the connection component, or may be formed in place by a processsuch as wire bonding while the connection component is in place on thechip. Restraining straps 232 are curved, but are shorter than signalleads 218. The restraining straps also may be provided as part of theconnection component or may be formed in place, as by wire bonding usinga relatively heavy-gauge wire. The assembly further includes a foamablelayer 270 disposed between the dielectric element and the chip. Thefoamable layer may include a thermoplastic or other polymeric materialin conjunction with a blowing agent adapted to form a gas upon exposureto heat. As described in greater detail in commonly assigned U.S.Provisional Patent Application 60/032,870, the disclosure of which ishereby incorporated by reference herein, such a foamable material willgenerate a gas under pressure and hence will introduce the gas underpressure between the opposed surfaces of the elements. For example, theblowing agent in the foamable material may be a heat-activated agent.

[0037] After the signal conductors and restraining straps are connectedbetween the two elements, foamable layer 270 is activated. The blowingagent introduces a gas under pressure between chip 250 and connectioncomponent 210, thus forcing the two elements vertically away from oneanother and deforming leads 218 to a more vertically-extensivedisposition. Here again, the restraining straps arrest the verticalmovement of the elements away from one another before the signal leadsare pulled taut.

[0038] Numerous variations and combinations of the features discussedabove can be employed. Thus, structural arrangements other than the viaand terminal structures discussed above with reference to FIGS. 1-3 canbe used to permanently secure the fixed or terminal ends of the leadsand straps to the dielectric structure. For example, the fixed ends ofthe leads and straps may be securely bonded to the dielectric structureitself. Also, the leads and straps may be electrically connected totraces or to other parts of the connection component which do notmechanically secure the fixed ends. The straps may be formed integrallywith potential reference planes such as ground or power planes inconnection component. Also, the methods and components according to theFIGS. 1-6 can be used with single chips, rather than with a wafer. Bothelements may includes chips or wafers. For example, the presentinvention can be applied to connect two chips to one another. Further,the methods and components discussed above can be used with assembliesof plural chips, which may remain united in the finished device to forma multichip module. In this case, the connection component and leads mayserve to interconnect the chips in the module. Also, the elements mayinclude microelectronic elements other than chips or wafers.

[0039] For example, in the assembly depicted in FIG. 10, one element 310is itself an assemblage including a package element 312 in the form of ametallic can having a flange 314 at its periphery, and further includinga semiconductor chip 316 and additional electrical elements 318 such ascapacitors, inductors, resistors or additional semiconductor chips. Thechip and other electrical elements have front surfaces 322 substantiallycoplanar with the front surface 324 of flange 314. The front surfaces ofthe flange, together with the front surfaces of the chip and of theother electrical elements cooperatively define the front surface ofelement 310. The other element 350 is a connection component including aflexible dielectric sheet 352 and one or more metallic potential planes354. Only one such potential plane is partially shown in FIG. 10.Connection component 350 further includes interconnect leads 356extending along one or both surfaces of the dielectric sheet, ordisposed within the sheet, and also includes terminals 358. Althoughonly a few such leads and terminals are depicted in FIG. 10, numerousleads would be provided in actual practice. Flexible signal leads 360are connected between connection component 350 and the chip 316 andother electrical components 318 of assemblage 310. The restrainingstraps 362 are provided only adjacent the periphery of the connectioncomponent, and are connected between a potential plane 354 of theconnection component and the flange 314 of the package. As described infurther detail in the aforementioned U.S. patent application Ser. No.08/690,532, the terminals and leads may be arranged to provide a“fan-out” arrangement, wherein the terminals 358 are disposed over asurface area larger than the area of chip 316. The interconnect leads356 and signal leads 360 may be arranged to connect the variouselectrical components to one another and to the appropriate terminals358.

[0040] During the process used to make this assembly, the terminals 358of the connection component are disposed in engagement with a flatsurface such as a support 370. Package 312 is urged toward the supportby a weight 372 or other device for applying a force in the verticaldirection without impeding horizontal movement of the package. A fluidsuch as a liquid encapsulant or foam is provided under pressure betweenassembly 310 and connection component 350, causing these elements tomove vertically away from one another. Here again, the restrainingstraps 362 constrain the relative motion of the elements. Thus, therestraining straps limit vertical movement of the elements, and causehorizontal movement of the elements relative to one another. Support 370maintains coplanarity of the terminals 358, and limits bulging of theflexible dielectric member 352.

[0041] In a further variant, the structural element which bears theleads and straps prior to assembly may be a semiconductor chip, wafer orother assemblage of plural chips. A unitary semiconductor wafer 401(FIG. 11) includes a plurality of chips 403. Each chip has numeroussignal leads 405 (FIG. 12) and restraining straps 407 disposed on thetop, contact-bearing surface of the chip. The signal leads and strapshave fixed ends connected to the structural element or wafer 401. Thesignal leads are connected to signal contacts of each chip, and henceare connected to internal signal connections 411 within the chip. Therestraining straps 407 are connected to constant-potential connectionsor reference contacts 409 such as power or ground connections. As in theembodiments discussed above, the free ends of the leads and straps arereleasably secured to the structural element. For example, the wafer mayhave a layer of a polymer such as polyimide on its top surfaces, and theleads and straps may be connected to the wafer in the same manner asdiscussed above with reference to leads connected to a dielectric film.

[0042] Although the invention herein has been described with referenceto particular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. A microelectronic assembly comprising: a first microelectronicelement including contacts on a contact-bearing face; a secondmicroelectronic element confronting said first microelectronic element;a plurality of vertically extended signal leads electricallyinterconnecting said first and second microelectronic elements; aplurality of vertically extended straps attached to said first andsecond microelectronic elements, wherein said straps are shorter thansaid signal leads for limiting vertical movement of said first andsecond microelectronic elements away from one another.
 2. Themicroelectronic assembly as claimed in claim 1 , wherein said signalleads are longer than said straps so that said signal leads do notconstrain vertical movement of said first and second microelectronicelements away from one another.
 3. The microelectronic assembly asclaimed in claim 1 , wherein said signal leads are partially curved. 4.The microelectronic assembly as claimed in claim 1 , wherein said strapsare substantially straight and fully extended for arresting verticalmovement of said first and second elements away from one another.
 5. Themicroelectronic assembly as claimed in claim 1 , wherein said straps arestronger than said signal leads.
 6. The microelectronic assembly asclaimed in claim 1 , wherein said straps are thicker than said signalleads.
 7. The microelectronic assembly as claimed in claim 1 , whereinsaid straps are less numerous than said signal leads.
 8. Themicroelectronic assembly as claimed in claim 1 , wherein said signalleads have fixed ends permanently attached to said secondmicroelectronic element and free ends bonded to the contacts of saidfirst microelectronic element.
 9. The microelectronic assembly asclaimed in claim 8 , wherein the fixed ends of said signal leads areelectrically interconnected with terminals accessible at a surface ofsaid second microelectronic element.
 10. The microelectronic assembly asclaimed in claim 1 , wherein said straps have fixed ends permanentlyattached to said second microelectronic element and free ends bonded tosaid first microelectronic element.
 11. The microelectronic assembly asclaimed in claim 10 , wherein the free ends of said straps are bonded tothe contact-bearing face of said first microelectronic element.
 12. Themicroelectronic assembly as claimed in claim 10 , wherein the free endsof said straps are bonded to one or more of the contacts of said firstmicroelectronic element.
 13. The microelectronic assembly as claimed inclaim 1 , wherein said first and second microelectronic elements includeconstant-potential connections and wherein at least one of said strapselectrically interconnects the constant-potential connections of saidfirst and second microelectronic elements.
 14. The microelectronicassembly as claimed in claim 1 , wherein some of said straps areconnected to a first potential plane serving as a power plane and othersaid straps are connected to a second potential plane serving as aground reference plane.
 15. The microelectronic assembly as claimed inclaim 1 , wherein said straps have larger cross-sectional areas thansaid signal leads.
 16. The microelectronic assembly as claimed in claim1 , wherein one of said first and second microelectronic elementsincludes a wafer having a plurality of semiconductor chips and the othersaid microelectronic element includes one or more connection components.17. The microelectronic assembly as claimed in claim 16 , wherein saidwafer is severable for forming individual units each including one ormore semiconductor chips and a part of said one or more connectioncomponents connected to the chips in such unit.
 18. The microelectronicassembly as claimed in claim 1 , wherein said first and secondmicroelectronic elements include opposing, horizontally-extendingsurfaces that confront one another, wherein said signal leads and saidstraps are disposed between said opposed surfaces.
 19. Themicroelectronic element as claimed in claim 10 , wherein the fixed endsof said straps and the free ends of said straps are offset from oneanother in a first horizontal direction, wherein said straps constrainmovement of said first and second microelectronic elements away from oneanother in said first horizontal direction.
 20. The microelectronicassembly as claimed in claim 1 , further comprising a compliant layerextending between said first and second microelectronic elements. 21.The microelectronic assembly as claimed in claim 20 , wherein saidcompliant layer covers at least some of said signal leads and straps.22. The microelectronic assembly as claimed in claim 1 , wherein saidstraps and said signal leads are made of a common electricallyconductive material.
 23. The microelectronic assembly as claimed inclaim 1 , wherein at least some of said straps are made of nonconductivematerials.
 24. The microelectronic assembly as claimed in claim 23 ,wherein one of said first and second microelectronic elements includes aconductive metallic sheet.
 25. The microelectronic assembly as claimedin claim 1 , wherein said first microelectronic element includes asemiconductor chip having rows of contacts along its edges and saidsecond microelectronic element includes a connection component having adielectric structural element with terminals thereon, and wherein saidsignal leads extend beyond peripheral edges of said dielectric element.26. The microelectronic assembly as claimed in claim 25 , wherein saidsignal leads have inner ends electrically connected to said terminals onsaid dielectric structure and outer ends connected to one of said chipcontacts.
 27. The microelectronic assembly as claimed in claim 26 ,wherein said straps have fixed ends permanently secured to saiddielectric element and free ends bonded to said chip.
 28. Themicroelectronic assembly as claimed in claim 25 , wherein said strapsare interspersed in the rows of said signal leads.
 29. A microelectronicassembly comprising: a first microelectronic element including contactson a contact-bearing face; a second microelectronic element juxtaposedwith said first microelectronic element; a plurality of verticallyextended signal leads electrically interconnecting said first and secondmicroelectronic elements; a plurality of vertically extended strapsattached to said first and second microelectronic elements, wherein saidstraps are shorter and stronger than said signal leads for limitingvertical movement of said first and second microelectronic elements awayfrom one another.
 30. The microelectronic assembly as claimed in claim29 , wherein said signal leads are longer than said straps so that saidsignal leads do not constrain vertical movement of said first and secondmicroelectronic elements away from one another.
 31. The microelectronicassembly as claimed in claim 30 , wherein said signal leads arepartially curved.
 32. The microelectronic assembly as claimed in claim29 , wherein said first microelectronic element includes a semiconductorchip and said second microelectronic element includes a dielectricsubstrate.
 33. The microelectronic assembly as claimed in claim 29 ,wherein one of said first and second microelectronic elements includes awafer having a plurality of semiconductor chips and the other of saidmicroelectronic elements includes one or more connection components. 34.The microelectronic element as claimed in claim 33 , wherein said waferis severable for forming individual units each including one or moresemiconductor chips and a part of said one or more connection componentsconnected to the chips in such unit.
 35. The microelectronic assembly asclaimed in claim 29 , wherein said first and second microelectronicelements include opposing, horizontally-extending surfaces that confrontone another, wherein said signal leads and said straps are disposedbetween said opposed surfaces.
 36. The microelectronic assembly asclaimed in claim 29 , wherein said straps are substantially straight andfully extended for arresting vertical movement of said first and secondelements away from one another.
 37. A microelectronic assemblycomprising: a first microelectronic element having rows of contactsalong one or more edges thereof; a second microelectronic elementjuxtaposed with said first microelectronic element, said secondmicroelectronic element having conductive terminals; a plurality ofsignal leads electrically interconnecting said first and secondmicroelectronic elements, wherein each said signal lead has an inner endelectrically connected with one of said terminals and an outer endelectrically connected with one of said contacts; a plurality ofrestraining straps having fixed ends permanently fastened to said secondmicroelectronic element and free ends connected to said firstmicroelectronic element, wherein said restraining straps are shorterthan said signal leads for limiting vertical movement of said first andsecond microelectronic elements away from one another.
 38. Themicroelectronic assembly as claimed in claim 37 , wherein said signalleads are longer than said straps sp that said signal leads do notconstrain movement of said first and second microelectronic elementsrelative to one another.
 39. The microelectronic assembly as claimed inclaim 37 , wherein said signal leads are partially curved.
 40. Themicroelectronic assembly as claimed in claim 37 , wherein said strapsare substantially straight and fully extend for arresting verticalmovement of said first and second microelectronic elements away from oneanother.
 41. The microelectronic assembly as claimed in claim 37 ,wherein said straps are stronger than said signal leads.
 42. Themicroelectronic assembly as claimed in claim 37 , wherein said strapsare thicker than said signal leads.
 43. The microelectronic assembly asclaimed in claim 37 , wherein said straps are less numerous than saidsignal lead.
 44. The microelectronic assembly as claimed in claim 37 ,further comprising a compliant layer extending between said first andsecond microelectronic elements.